The present invention relates to a method and an apparatus for improving the running characteristics of a running gear of a rail vehicle which is provided with a plurality of individual wheels and the traction motors of which are supplied with power on a wheel block by wheel block basis by two open-loop/closed-loop control devices.
Rail vehicles comprise car body and running gear. The running gear has two tasks: it assumes the guidance of the vehicle in the gage channel of the track, and it has to protect the car body against impacts.
Track guidance is ideal if the vehicle exactly follows the center of the track. The track guidance behavior of the running gear better approximates ideal track guidance the quicker deviations from the track axis are corrected.
The track guidance behavior can be quickly assessed on the basis of just two parameters:
the reduction of transverse offset and PA1 the reduction of tilting in the track.
Transverse displacements are related to forces while the reduction of tilting relates to a turning moment. The latter in turn is related to forces, which produce the desired moment by a lever arm about a suitable pivot point or as a force couple.
In a wheel/rail contact surface forces occur which can be used for guiding. Depending on the physical effect, a distinction is to be drawn between two fundamentally different types of forces.
When the wheel slides transversely there is a first frictional force at the stand-up point of the wheel in relation to the rail. When the wheel slides longitudinally also at the stand-up point of the wheel in relation to the rail there is a second frictional force. The product of relative speed and frictional force constitutes a frictional power loss. It is manifested as a resistance to track guidance and is converted in wheel-rail contact into heat and wear on the wheel and rail. Rolling noise is also closely associated with it.
In the article "Aspekte zur Spurfuhrung" (Aspects of track guidance), printed in the journal "ZEV-Glas.Ann." 114 (1990), No. 1/2, pages 24 to 29, various track guidance principles are presented and investigated with regard to track guidance behavior.
This article discloses a "wheel block" track guidance principle. In the case of a wheel block, two individual wheels are used, which are not arranged next to each other but one behind the other. The individual wheels arranged one behind the other prove to be virtually ideal for the correction of tilting. Traverse frictional forces of the same magnitude act on the two wheels of the inclined wheel block due to the same tilted running angle .delta.. With respect to the pivot point, they compensate for the turning moments occurring as a result. From this aspect, the wheel block is always in a state of equilibrium. From any desired position of the phase diagram of the wheel block, the transverse deflections and any tilting are reduced very quickly to values around zero. The wheel block reduces both the transverse offset and tiltings and consequently reduce wear by means of profile lateral forces. The wheel block track guidance principle would come very close to the ideal if there were no longitudinal frictional forces, as is the case with driven wheels.
EP 0 374 290 A1 discloses a rail vehicle which comprises on both sides along the longitudinal vehicle axis a predeterminable number of individual wheels which can be swiveled by steering. Track-error-free steering of each individual wheel in all bend regions is achieved by providing a rail-path measuring device, which measures the deviation of a vehicle axis from the path of the rail and which, depending on the measured deviations, generates a steering signal for each individual wheel independently of the other. Consequently, in any position on a bend, each individual wheel is always correctly steered in such a way that track errors can no longer occur.
The above-mentioned article also discloses the "wheelset" track guidance principle. Wheelsets have two wheels, which are fixedly connected to the wheelset shaft. This necessarily causes the wheels to rotate with the same rotational speed. In addition, the two wheels inevitably experience the same tilting with respect to the track if the wheelset is turned about a vertical axis. A transverse offset directly initiates a likewise undesired tilting owing to longitudinal frictional forces occurring. Just as a transverse deflection leads to tilting, conversely tilting results in a transverse deflection. The two movements are closely linked to one another. They alter as a function of each other in a constant state of change. Once deflected, the wheelset no longer comes to rest. As known, a wheelset moves in a wave form in the gage channel (sinusoidal motion), striking against the wheel flange being unlikely on straight sections of track.
When traveling around bends, in an ideal case the wheel planes should be tangential to the rail. Nevertheless, rolling of the wheels without any constraining forces is guaranteed only if the rolling radii of the wheels are relatively equal to the arc lengths of the two running rails. This permits a transverse offset. The necessary difference between the rolling radii on account of the angle of taper or conicity of the wheel profiles of the two wheels becomes the known rolling condition of the wheelset. If, owing to the track guidance, the necessary difference between the rolling radii is greater than the possible difference on account of the wheel profile, the wheels can no longer roll without any constraining forces. In other words the wheel on the outside of the bend therefore turns too slowly, the wheel on the inside of the bend turns too quickly. Due to the different longitudinal frictional forces, there occurs with respect to the vertical axis a turning moment, which turns the running gear, also known as the bogie, out from the arc. The counter-moment can be applied only by the transverse frictional forces or by a striking of the wheel flange, with corresponding wear.
A bogie with rigid axle behavior displays good running characteristics on straight sections (classical sinusoidal motion), but constant striking may not be prevented on curved sections if the rolling condition is no longer satisfied owing to too small an arc radius.